This particular battle, though, is not being fought in the nation’s pharmacies, where giant drug companies’ profits are being co-opted by nimbler competitors offering generic — and much cheaper — versions of popular drugs.

Instead, the fight has shifted to Sarabian Farms’ 200 acres of peaches, plums and nuts in California’s Central Valley — and the thousands of farms nationwide that use $6 billion worth of herbicides a year.

With 70 percent of U.S. weed killer patents expected to expire by 2010, an increasing number of smaller competitors are racing to compete with behemoths such as Monsanto Co. and Dow Agrosciences for a share of that market.

“Generic makers will never gain complete control of the market,” said agricultural chemical consultant Robert Ehn, who’s client roster includes generic companies. “But they will be big players.”

Already, a patent on the world’s most popular herbicide — Monsanto Co.’s Roundup — has expired, forcing the St. Louis biotechnology company to slash prices dramatically to hang on to its dominant market share.

Monsanto’s total sales last year fell one percent to $5.5 billion, due in part to the price drop. The company expects sales to be even more sluggish this year, though it also blames a Midwestern drought and Latin American fiscal crisis as aggravating factors.

Monsanto has sued at least one generic competitor, accusing Chemical Product Technologies, which makes Clearout, of violating other Monsanto patents. The Georgia company countersued, accusing Monsanto of antitrust behavior.

But nowhere is the fight nastier than in California, over oryzalin, an herbicide produced by Indiana-based Dow Agrosciences that is used by nut growers, fruit tree farmers and others to kill weeds such as crabgrass before they sprout.

California, the nation’s most productive agricultural state, consumes half the oryzalin sold nationwide.